Ultrahigh pressure equation of state of CaS to 1.5 Mbar

Abstract

Energy Dispersive X-ray Diffraction (EDXD) was performed at room temperature to gather structural data on CaS between approximately 1.7 GPa to nearly 150GPa. In these experiments, CaS retained the B1 structure up to approximately 40 GPa above which it began to transform to the B2 structure. The B2 structure remained stable to the highest pressure reached, 149 GPa, where the relative volume V/V₀ was 0.490. Previous studies on CaS extended only up to 52 GPa, which is barely 10 GPa after the B1 phase changes to the B2 structure. Thus it was not possible to accurately extrapolate the equation of state (EOS) for the B2 phase region to significantly higher pressures. In the present study EOS data for CaS was collected to 150 GPa and no other structural change was observed. EOS parameters for the B1 and B2 phase regions agree well with values reported in the literature.     

Structural transitions in hydrogen and deuterium at ultrahigh pressures

Abstract

Raman measurements indicate that normal hydrogen and deuterium compressed in a diamond-anvil cell at 77 K undergo phase transformations at 145 (±l5) GPa and 190 (±l20) GPa, respectively. The new observations reported for deuterium indicate that the transition in both isotopes is a structural change not associated with a simple rotational ordering mechanism. The possibility of a structural transition driven by band-gap closure is discussed.     

Anomalous compressibility and metallization of deuterium and hydrogen at high pressures

The high compressibilities recorded in experiments on liquid-deuterium compression and the significant scatter of experimentally measured densities in the region of anomalous compressibilities are explained by the manifestations of an unusual dielectric-metal phase transition: from a dense molecular gas to a liquid-metal atomic gas. This transition has previously been described by us and called the dissociative phase transition (DPT). The dissociative equilibrium curves, the isotherms, the DPT binodal, and the Hugoniot adiabat have been calculated. The DPT has been shown to be a transition of a new, non-van der Waals type.     

Rotational Raman scattering of hydrogen and deuterium for calibrating Thomson scattering devices

Rotational Raman scattering cross sections of hydrogen and deuterium were measured and calculated for ruby and neodymium laser wavelengths. They are suited for calibrating Thomson scattering of KeV plasmas.     

Raman scattering measurements of molecular hydrogen in a low-density, arc-heated plasma

Raman scattering measurements of molecular hydrogen density and temperature were made in a low-density, arc-heated plasma flow. Pulsed-laser excitation was used to improve the signal-to-noise ratio in this high-background environment. Quantum-limited detection was achieved through the use of gated photon counting and a high-power Nd:YAG laser. Radial profiles of rotational temperature and density at the exit plane were measured for five power levels. In all cases the profiles were asymmetric about the centerline. The rotational temperatures were compared with the translational temperatures of atomic hydrogen from LIF studies and found to be slightly lower. This result suggests that this flow, like the cold flow, is not in translational-rotational equilibrium.     

Lattice expansion of niobium and tantalum due to dissolved hydrogen and deuterium

The volume change of niobium and tantalum due to interstitially dissolved hydrogen and deuterium has been determined by means of X-ray Bragg scattering. The volume increase in niobium is the same for hydrogen and deuterium $\text{δν=(0.174±0.005)Ω}$(Ω: atomic volume). A small isotope effect has been observed in the case of tantalum, $\text{Δν=(0.155±0.002) Ω}$ for hydrogen and $\text{Δν=(0.143±0.005)Ω}$ for deuterium.     

Precision measurement of antiprotonic hydrogen and deuterium X-rays

X-rays from antiprotonic hydrogen and deuterium have been measured at low pressures. Using the cyclotron trap, a 105 MeV/c antiproton beam from LEAR was stopped with an efficiency of 86% in 30 mbar hydrogen gas in a volume of only 100 cm³. The X-rays were measured with Si(Li) detectors and a Xe-CH₄ drift chamber. The strong interaction shift and broadening of the Lyman transition and the spin-averaged 2p width in antiprotonic hydrogen was measured with unprecedented accuracy. The triplet component of the ground state in antiprotonic hydrogen was determined for the first time.The authors would like to thank the LEAR staff for their efforts in providing the antiproton beam. The help of P. Gauss from the CERN cryogenic group and of P. Zettwoch from the PS workshop is gratefully acknowledged. We wish to thank K.-P. Wieder for his help with the drawings. This work is part of the Ph.D. thesis of one of us (K.H., University of Karlsruhe, 1990).     

Shock-wave compression of hydrogen to pressures of 65 GPa

The results of experiments on determining the shock-wave compression of initially solid hydrogen (protium) in the pressure range from 17 to 66 GPa are reported. The data have been obtained by using spherical explosive charges. Pressure in samples is created by the impact of a steel striker accelerated to maximum velocities of 23 km/s. Gaseous protium is converted to the solid state using a special cryogenic cooling system.     

Electromigration and permeation of hydrogen and deuterium in silver

A steady state flow technique was used to measure the effective charge number (Z*) and permeability (N) of hydrogen and deuterium in silver. Over the range of temperature (485–720°C) and pressure (220–750 torr) the effective charge number is a constant. The interstitial impurity migrates in the direction of the electron wind with Z_H* = ?6·8 and Z_D* = ? 18. The values of Z* are of the same order as self-electromigration but the size of the isotope effect is surprising. The quantum theories used to explain the isotope effect for hydrogen electromigration in Fe and Ni appear to fail here. In order to determine the effective charge number is was necessary to measure the permeability. For both H₂ and D₂, the permeability in silver follows the equation N = N_O exp(? Q/RT) where N_0D = 2·39 ± 0·40, Q_D = 14400 ± 300, N_OH = 2·86 ± 0·70 and Q_H = 14200 ± 500. Here Q is in units of cal/mol and N is in units of cc(ntp)/(sec - atm² - cm) The isotope effect ratio N_H/N_D = 1·25 was smaller than the classically expected value of (2)^1/2, but could be explained by the theory of Ebisuzaki, Kass and O'Keeffe.     

Raman spectra of alcohols: Intensity measurements

The peak, integrated and standard intensities of some prominent Raman lines in twelve alcohols are estimated. The standard intensities of the lines due to some characteristic bonds in various alcohols are compared and large variations observed.     

Cross-section measurement of charged-pion photoproduction from hydrogen and deuterium

We have measured the differential cross section for the gamman-->pi(-)p and gammap-->pi(+)n reactions at theta(c.m.)=90 degrees in the photon energy range from 1.1 to 5.5 GeV at Jefferson Lab (JLab). The data at E(gamma) greater, similar 3.3 GeV exhibit a global scaling behavior for both pi(-) and pi(+) photoproduction, consistent with the constituent counting rule and the existing pi(+) photoproduction data. Possible oscillations around the scaling value are suggested by these new data. The data show enhancement in the scaled cross section at a center-of-mass energy near 2.2 GeV. The cross section ratio of exclusive pi(-) to pi(+) photoproduction at high energy is consistent with the prediction based on one-hard-gluon-exchange diagrams.     

Metallization degree of hydrogen at a pressure of 1.4 Mbar and a temperature a 3000 K

The electrical resistivity of liquid metallic hydrogen at a temperature of 3000 K and a density of 0.35 mol/cm³ is calculated. Hydrogen is considered as a three-component system consisting of electrons, protons, and neutral hydrogen atoms. The second order of perturbation theory in electron-proton and electron-atom interactions is used to determine the inverse relaxation time for electric conductivity. The Coulomb electron-electron interaction is taken into account in the random phase approximation and the exchange interaction and correlation of conductivity electrons are included in the local-field approximation. The model of hard spheres is used for the proton and atomic subsystems. The concentration of the electrically neutral atomic component proved to be significantly lower than the value assumed by the discoverers of metallic hydrogen.     

Quasi-isentropic compressibility of a strongly nonideal deuterium plasma at pressures of up to 5500 GPa: Nonideality and degeneracy effects

We report on the experimental results on the quasi-isentropic compressibility of a strongly nonideal deuterium plasma that have been obtained on setups of cylindrical and spherical geometries in the pressure range of up to P ≈ 5500 GPa. We describe the characteristics of experimental setups, as well as the methods for the diagnostics and interpretation of the experimental results. The trajectory of metal shells that compress the deuterium plasma was detected using powerful pulsed X-ray sources with a maximal electron energy of up to 60 MeV. The values of the plasma density, which varied from ρ ≈ 0.8 g/cm³ to ρ ≈ 6 g/cm³, which corresponds to pressure P ≈ 5500 GPa (55 Mbar), were determined from the measured value of the shell radius at the instant that it was stopped. The pressure of the compressed plasma was determined using gasdynamic calculations taking into account the actual characteristics of the experimental setups. We have obtained a strongly compressed deuterium plasma in which electron degeneracy effects under the conditions of strong interparticle interaction are significant. The experimental results have been compared with the theoretical models of a strongly nonideal partly degenerate plasma. We have obtained experimental confirmation of the plasma phase transition in the pressure range near 150 GPa (1.5 Mbar), which is in keeping with the conclusion concerning anomaly in the compressibility of the deuterium plasma drawn in [1].